Rotary fluid handling machinery such as pumps, centrifugal compressors, radial in-flow expansion turbines and unitary expander-driven compressor assemblies generally employ a wheel mounted on a rotatable shaft positioned within a stationary housing. The wheel is generally composed of a plurality of curved flow paths establishing flow communication between essentially radially directed and axially directed openings. A working fluid, such as gas at high pressure, is caused to pass through these curved flow paths and, as it so passes through, energy is transferred, such as by expansion of gas, from the working fluid to the wheel which is caused to rotate thereby rotating the shaft and transferring the energy to a point of use.
One problem encountered in the use of such rotary machinery is the loss of working fluid before its energy can be transferred to the wheel. Such loss could be, for example, high pressure gas leakage between the front and back sides of the wheel and the stationary housing. Working fluid which is so lost does not pass through the curved flow paths and thus there is experienced an inefficiency in the operation of the rotary machinery.
In order to reduce this high pressure fluid loss, rotary fluid handling machinery is often equipped with annular seals on the back and on the front of a shrouded wheel. The back and front annular seals are generally an equal radial distance from the shaft so that the high pressure working fluid sealed by these seals exerts its force over equivalent areas in opposing directions on the back and front of the wheel. In this way net thrust forces on the shaft caused by the sealed high pressure working fluid are minimized. The front annular seal is generally positioned between the wheel and housing at essentially the eye diameter of the wheel and as mentioned, the back annular seal is at the same or nearly the same radial distance from the shaft as is the front annular seal.
Some rotary fluid handling machinery are not equipped with a front annular seal. In this case there will always be generated some net thrust force on the shaft due to the unbalance of forces on the wheel by the fluid. This thrust force is handled by thrust bearings which oppose the thrust force and keep the shaft axially aligned. In order to minimize the force on the thrust bearings, the back annular seal is positioned at as great a radial distance from the shaft as is practicable. This minimizes the pressure differential between the back and front of the wheel and thus minimizes the thrust forces generated by this pressure differential.
A problem of rotary fluid handling machinery is the loss of working fluid by leakage through the annular seals. One way to reduce this leakage is to position the seals as close to the shaft in a radial direction as possible. As is well known the closer is the annular seal to the shaft, the lesser is the area available for working fluid leakage and thus the lesser is the leakage flow rate experienced. However, the position of the front annular seal is essentially fixed at about the eye diameter since this is the only practical position for the front seal to be effective. Positioning the back annular seal at a radial distance from the shaft less then the radial distance of the front seal in order to reduce working fluid leakage through the back seal will result in a pressure difference, precipitating the net thrust force problem described earlier. One way to address such a problem is to design the thrust bearings to undertake a very high load. However this is costly and also difficult to accomplish.
It is therefore an object of this invention to provide an improved rotary fluid handling apparatus.
It is another object of this invention to provide an improved rotary fluid handling apparatus wherein fluid leakage past the back annular seal is minimized.
It is another object of this invention to provide an improved rotary fluid handling apparatus wherein fluid leakage past the back annular seal is minimized while avoiding the generation of large net thrust forces.
It is yet another object of this invention to provide an improved rotary fluid handling apparatus wherein the net thrust force on the thrust bearings is essentially zero.